Magnetic bearings are used in industry to enable the rotor of a rotary machine to rotate in contactless manner. A magnetic bearing may be used directly in environments for processing and/or extracting gases that are under pressure, corrosive, and hot. On the stator, such a bearing is made up of stacks of magnetic laminations on which the electrical coils are placed that are used for generating the magnetic field necessary for levitation of the rotor. That type of machine is well known and described, for example, in Patent EP 1 395 759 filed in the name of the Applicant. Since the resulting assembly is for placing in the potentially electrically conductive flow of corrosive gas, it is necessary to protect the copper conductors of the electrical coils from the environment, and to insulate the copper wires from one another and from ground.
The compatibility of the insulation of the copper wires with the environment is a recurrent problem in industrial applications, in particular in gas fields in which the composition of the gas can vary over time and cannot be kept fully under control. In addition, adding process fluid, e.g. mono-ethylene glycol, can degrade the quality of the insulation and cause a failure in the rotary machine as a whole. In addition, connections between coils are necessary in order to implement the electrical circuit of the machine, but such connections represent weak points in the electrical insulation, because, under pressure, they might be grounded by fluid finding its way to the copper conductor. Such grounding should be avoided at all cost because it causes total system failure, and thus causes the machine to shut down.
One solution to that problem of insulating electrical connections consists in using insulation made up of various taped, non-sealed layers that are impregnated with an electrical insulation resin that is typically an epoxy resin. The purpose of that resin is to insulate the connection electrically from the surrounding environment, and to protect the copper conductors of said connection chemically from the corrosive gas by serving as a mechanical barrier.
In view of the wide variety of chemical atmospheres, of pressures, and of temperatures encountered in industrial applications, it is very difficult to find an impregnation resin that can withstand such a variety of stresses. In addition, in view of the difficulty of identifying all of the degradation phenomena of known electrical resins and of their interactions with the elements of the gas, validation of the chemical protection requires testing that is complex and costly to put in place, on installations that are, in practice, not very commonplace.
That is why, in its Application EP 2 410 533, the Applicant proposes that this conventional principle of protecting conductor wires with impregnation resin be replaced with an insulation system that is extruded directly over each conductor wire and that is sealed and continuous to the outlet of the machine, advantageously making it possible to make sealed connections by thermoplastic fusion.
That insulation system is fully satisfactory as regards the inner connections. Unfortunately, it does not solve the problem of the exit electrical connection on the sealed feed-through connector. Such connections have very little protection from moisture, which appears as a source of possible insulation break-down in highly corrosive gas-processing environments.